Striker Emile Sinclair is out for four weeks with a hamstring strain, midfielder Richard Butcher is sidelined for four to six weeks with a knee injury and defender Shaun Brisley out for four months with a hip injury.
Forward Ricky Sappleton is still working back to fitness after a knee problem and is not yet ready for a first-team return despite playing a couple of reserve games.
Midfielder Izak Reid should be available after a groin problem and defender Paul Morgan is set to return after missing last weekend`s defeat at Lincoln with a thigh strain.
After two successive defeats, Simpson may look to ring the changes.
Mark Creighton could return to Oxford's starting line-up.
The 29-year-old, who has recently returned from a toe injury, played for the reserves in midweek and could play after being named among the substitutes last week.
Jake Wright and Damien Batt are on the road to recovery from back and ankle injuries respectively, although the game will come too soon for them.
Rhys Day will not be available after agreeing to join Blue Square Bet Premier club Mansfield on a three-month loan deal.
The Us have acclimatised well to life in npower League One and will be hoping to move towards the play-off places with victory over the Silkmen.
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